The present invention relates to GPS/GNSS receivers. More specifically, the present invention relates to time transfer in GPS/GNSS receivers using weak GPS/GNSS signals.
The use of GPS/GNSS signals for time transfer at the sub-microsecond level is a well-established art. However, most conventional methods depend on the ability of a GPS/GNSS receiver to accurately demodulate timing information from the received GPS/GNSS signal. This implies that the signal must be strong enough to keep the demodulated bit error rate acceptably small (for example, less than about 10−5), which can be guaranteed only if the received signal power is above approximately −148 dBm. Accordingly, it is difficult to establish sub-microsecond time transfer using very weak GPS/GNSS signals suffering severe attenuation, such as those received indoors or in urban canyons.